In recent years, various light source devices have been developed which use a semiconductor light emitting element such as a laser diode as an excitation light source.
The light source device can be configured to irradiate a light emitting section including a plurality of phosphor particles from which light with different peak wavelengths is emitted, with excitation light from an excitation light source, and thus fluorescence of each of plural colors is emitted from the light emitting section. White light including the fluorescence of each of plural colors (for example, red, green, and blue) can be emitted from the light source device as illumination light.
Japanese Unexamined Patent Application Publication No. 2012-114040 (published on Jun. 14, 2012) describes a light source device capable of improving a color reproduction property. A light emitting section (phosphor section) is formed by stacking a plurality of layers, each layer having a phosphor material emitting fluorescence of a corresponding color in the light source device of Japanese Unexamined Patent Application Publication No. 2012-114040.
The expression “having a low color reproduction property” described in Japanese Unexamined Patent Application Publication No. 2012-114040 means a problem in that it is difficult to accurately reproduce the color of an object irradiated with white light, since bluish green light or red light are insufficiently emitted in the light-emitting spectrum of white light (refer to the paragraph [0040] in Japanese Unexamined Patent Application Publication No. 2012-114040).
Japanese Unexamined Patent Application Publication No. 2013-229438 (published on Nov. 7, 2013) describes a light source device which has a color conversion molding with small limitation on thickness or shape.
Japanese Unexamined Patent Application Publication No. 2011-181381 (published on Sep. 15, 2011) describes a light source device in which it is possible to suppress color variation in emitted light resulting from blue laser light radiated from a laser light source and reflected by a metal plate surface having no phosphor around the phosphor (to suppress a circumference of a light distribution pattern being blue-colored).
Japanese Unexamined Patent Application Publication No. 2008-226492 (published on Sep. 25, 2008) and Japanese Unexamined Patent Application Publication No. 2009-44137 (published on Feb. 26, 2009) describe light emitting devices in which a light emitting section is formed by stacking a plurality of layers, each layer having a phosphor material, as in Japanese Unexamined Patent Application Publication No. 2012-114040.
There is a case where uneven white light is obtained when excitation light excites a light emitting section in the light source device in which white light is obtained as illumination light by mixing fluorescence of a plurality of different light-emitting peak wavelengths from each other.
However, a structure for suppressing variation of the illumination light on a surface of the light emitting section is neither described nor suggested in Japanese Unexamined Patent Application Publication No. 2012-114040, Japanese Unexamined Patent Application Publication No. 2013-229438, Japanese Unexamined Patent Application Publication No. 2008-226492, or Japanese Unexamined Patent Application Publication No. 2009-44137. A structure for suppressing variation of the illumination light resulting from reflection of blue laser light on a surface of a metal plate around the phosphor section is disclosed, but a structure for suppressing variation of the illumination light resulting from a plurality of phosphor materials is neither described nor suggested in Japanese Unexamined Patent Application Publication No. 2011-181381.
Accordingly, there is a concern that it is difficult to suppress variation of the illumination light in the light emitting device having a light emitting section formed of a plurality of phosphor materials.